1. Field of Invention
The present invention relates to the transfer of data in an interactive video-on-demand (VOD) distribution system. More particularly, the invention relates to a method of providing data between fiber-channel arbitrated loop arrays at each of a plurality of head-ends in an information distribution system.
2. Description of the Background Art
In an interactive information distribution system, such as an interactive video-on-demand (VOD) distribution system, a plurality of cable head-ends are utilized to serve as video content distribution points, for designated xe2x80x9cneighborhoodsxe2x80x9d of subscribers. A request for video information, such as a movie, is made by selecting from a menu, a title displayed on a subscriber""s monitor. After selection by the subscriber, the request is sent back, via an access network, to the local head-end supporting such subscriber. The requested video is then transmitted from the head-end to the subscriber for viewing.
A typical head-end comprises a VOD server system, having subsystems that interface with each other to manage, store and distribute the video content. The subsystems include a video stream server, video content storage devices, and host workstations for interfacing with various management software modules. Memory buffer boards, such as Compact PCI type boards, are also utilized by each subsystem for temporarily storing data, before streaming the data across an access network, and to the subscribers.
The server is typically, a parallel processing computer system, capable of accepting information requests from the management software modules, recalling that information from memory, and generating a plurality of video streams containing packetized video information. The video information may be stored within the computer system""s disk drive array, off-line storage system such as an optical disk library, and/or is available from a digital or analog real-time program feed.
One function of an information video distribution system, is to transfer and replicate data between each of the head-ends. As subscriber viewership rises, there is a need to efficiently utilize bandwidth for transferring and storing such video data between the storage devices at each head-end.
To replicate video content from storage devices on one fiber channel arbitrated loop (FC-AL) to storage devices on other FC-AL""s, requires the data to be transferred or replicated from a single source FC disk loop, to a first memory buffer board within one of the sub-systems of the server. The memory buffer board of the source subsystem, then transfers the data across a video switch to a receiving memory buffer board, in a subsystem of another server. Once the data has been stored on the receiving memory buffer board, the data is written to the appropriate disk drives on a second destination FC disk loop.
A disadvantage of transferring data from one memory buffer board to another memory buffer board in a different sub-system, is that such data transfer consumes a large portion of the available bandwidth on both memory buffer boards. Furthermore, the available bandwidth of a video switch, which links the servers at each head-end across an inter-server network, is also inefficiently utilized. Thus, the bandwidth on the memory buffer boards, which would normally be used for transmitting streams of information to the subscribers, is thereby reduced.
As subscriber viewership grows, the head-end servers and subsystems have a greater level of activity. The processing circuitry and memory are processing more information, which results in a higher latency at each the head-end, for responding to the individual subscriber requests. In such an environment where demand is great, and expectations by the subscriber are for an instantaneous and seamless service, there becomes a need to implement a means to efficiently transfer or replicate such video content, without the tradeoff of decreasing the bandwidth necessary to stream such information to the subscribers.
The disadvantages heretofore associated with the prior art are overcome by the present invention of a method and apparatus of utilizing two independent fiber channel arbitrated loops for moving, replicating and storing video information in an interactive video information system. A plurality of servers, are each comprised of a plurality of server modules. Each server module comprises a plurality of fiber channel (FC) disk drives, coupled by a xe2x80x9clocalxe2x80x9d port to a first independent, xe2x80x9clocalxe2x80x9d fiber channel arbitrated loop, to create a xe2x80x9cvirtual FC disk drivexe2x80x9d, within each server module. The plurality of FC disk drives on each of the plurality of server modules are also coupled to a second independent, xe2x80x9cbackupxe2x80x9d fiber channel arbitrated loop, via a xe2x80x9cbackupxe2x80x9d port on each FC disk drive. By utilizing two independent FC loops in this configuration, data may be sequentially transmitted from a first server module, across the backup FC loop, to a second server module.
In a preferred embodiment of the invention, each server comprises eight server modules, each server module having eight FC disk drives respectfully coupled to an independent local FC loop, via the local port of the disk drive. Each local FC loop also has an associated FC controller and processing circuitry, to allow the server module to transfer and receive information. The backup FC loop comprises a xe2x80x9cbackupxe2x80x9d FC controller to control the flow of data between the disk drives on the backup FC loop. Thus, a head-end server comprises a group of server modules linked together by the independent backup FC loop, to form a xe2x80x9cvirtual serverxe2x80x9d.
A method for transferring and replicating information between one server module to another server module, is accomplished by utilizing the backup FC loop as a physical medium between the disk drives in each of the server modules. The backup FC loop allows video information to be serially transferred from the storage devices on each local FC loop, without losing any of the bandwidth from having to utilize memory buffer cards to temporarily store video information or any of the video switch bandwidth. An advantage of utilizing two independent FC loops, is that the memory buffers on each of the subsystems are no longer required as a shared resource for storing data when streaming data to the subscribers, and when transferring data back and forth between server modules.
Furthermore, by connecting each server to a FC switch and an inter-server network, content may be moved from one server to another, in a similar manner as between two or more server modules. This has an additional benefit, in which a secondary storage device (e.g., DLT (digital linear tape drive)) is not needed as frequently for loading video information, since the video information would only have to be retrieved once from the secondary storage device, when replicating such video information. Thereafter, the video content may be copied from each server module on one server, to server modules having available storage capacity on other servers, which are coupled through an inter-server network and the FC switch.